Method of producing polishing pad-use polyurethane foam and polyurethane foam

ABSTRACT

A production method comprising the step of charging prepolymer, a foaming agent and an active hydrogen-containing compound in specified amounts into a tank and foaming/mixing them for a specified time by a mixer, and the subsequent step of pouring the mixture liquid into a metal mold.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing a polishingpad-use polyurethane foam and a polyurethane foam produced by such amethod.

2. Description of the Related Art

With respect to a polishing method for smoothing a wiring formation faceon a semiconductor substrate efficiently with high precision, a CMP(Chemical Mechanical Polishing) method has been adopted. This method isa polishing method in which chemical functions and mechanical functionsare utilized in a combined manner, and makes it possible to flatten thesemiconductor substrate (wafer surface) over a wide range.

Some of polishing pads to be used in this CMP method are formed by apolyurethane foam so that fine recessed sections are formed on thesurface with polishing slurry being maintained therein.

With respect to a known technique for a producing method of such apolishing pad-use polyurethane foam, for example, Japanese PatentApplication Laid-Open No. 11-322877 has disclosed a producing method. Inthis producing method, upon mixing and stirring two solutions of anisocyanate-terminated prepolymer and an active hydrogen-containingcompound, unfoamed heat-expansive fine hollow spherical particles(hollow balloons) are preliminarily added and mixed in either of theprepolymer and the active hydrogen-containing compound, and by utilizingreaction heat released when the two solutions are allowed to react witheach other and cured or externally-applied heat, the unfoamedheat-expansive fine hollow spherical particles are finely foamed in theurethane molded product so that the molded product is allowed to containthe heat-expanded fine hollow spherical particles.

Moreover, Japanese National Publication of International PatentApplication No. 8-500622 has disclosed a producing method as anotherknown technique. In this producing method, an isocyanate-terminatedprepolymer and an active hydrogen-containing compound (MBOCA) togetherwith expanded fine hollow particles are simultaneously put into aspecial mixer in which the fine hollow particles are fully kneaded in ashort reaction time, and evenly dispersed and mixed.

However, the hollow balloons of this expanded type are a powder materialhaving a specific gravity of about 0.04 g/cm³, and it is difficult tofully knead and evenly mix the hollow balloons in this state with theurethane solution. The reason for this is explained as follows: sincethere is a great difference in density between the reaction solution andthe hollow balloons, the hollow balloons tend to float up during thecuring process, causing a difficulty in forming an even product. Withrespect to the hollow balloons of this expansive type, void balloonswith holes are contained in a pre-expansion stage, and dusts, which haveadhered to pipes and the like in the expansion process to be depositedthereon, and are burned through heat to form hard foreign matters, arealso contained therein. Such hardened foreign matters remaining inurethane tend to cause scratches in the polishing process, resulting ina serious problem. In this manner, a producing process of a polyurethanefoam by the use of hollow balloons tends to cause adverse effects.

The present invention has been devised to solve the above-mentionedproblems, and its objective is to provide a producing method of apolishing pad-use polyurethane foam, which can produce a polyurethanefoam that is evenly formed and less susceptible to deviations inspecific gravity through processes without using hollow balloons.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned problems, the method of aproducing polishing pad-use polyurethane foam in accordance with thepresent invention has the steps of: charging a first component, afoaming agent and a second component that reacts with the firstcomponent to form polyurethane in specified amounts into a tank andfoaming/mixing them for a specified time by a mixer, and after theabove-mentioned step, pouring the mixed solution into a mold so as toreact with one another to be cured.

With this arrangement, the first component (for example, prepolymer),the foaming agent and the second component are charged into a tank andfoamed and mixed by a mixer for a predetermined time. Thus, a gas suchas air is forcefully involved therein so that the mixture is finelydispersed and foamed. In other words, different from the conventionaltechnique, it becomes possible to carry out a foaming process through amethod without using hollow balloons. The inventors of the presentinvention have found that the amounts of the first component, thefoaming agent and the second component (for example, an activehydrogen-containing compound) to be charged into the tank and thestirring time are appropriately controlled so that a polyurethane foamthat is evenly formed and less susceptible to deviations in specificgravity is prepared.

With respect to the charging process of the first component, the foamingagent and the second component into the tank in the abovementionedmixing process, these materials may be charged simultaneously, or someof the respective elements are first charged into the tank, and stirredand mixed, and after a lapse of predetermined time, the rest of theelements may be charged and stirred.

Here, with respect to the method of producing a fine-bubble polyurethanefoam by using the producing method of the present invention, thefollowing two methods are proposed:

(1) Prepolymer Method

A method, which produces a fine-bubble polyurethane foam by mixing afirst component containing an isocyanate-group-containing compound and asecond component containing an active hydrogen-containing compound, isprovided with the steps of: adding a silicon-based nonionic surfactanthaving no hydroxide group to at least either of the first component andthe second component; stirring the component to which the surfactant hasbeen added with a non-reactive gas so that the non-reactive gas,preferably, air, is dispersed as fine bubbles therein to form a bubbledispersion solution; and mixing the rest of the components in the bubbledispersion solution to be cured.

In this method, more specifically, an isocyanate prepolymer withisocyanate group terminals is used as the first component, and afterthis component has been formed into a bubble dispersion solution, thesolution is crosslinked by using a chain-extension agent such as MBOCAserving as the second component; or a prepolymer with hydroxide groupterminals is used as the second component, and after this component hasbeen formed into a bubble dispersion solution, the solution iscrosslinked by using an isocyanate compound such as diphenylmethanediisocyanate serving as the first component.

(2) One-shot Method

A method, which produces a fine-bubble polyurethane foam by mixing afirst component containing an isocyanate-group-containing compound and asecond component containing an active hydrogenv-containing compound, isprovided with the steps of: adding a silicon-based nonionic surfactanthaving no hydroxide group to at least either of the first component andthe second component; mixing and stirring the first component and thesecond component with a non-reactive gas, preferably air, so that thenon-reactive gas is dispersed as fine bubbles therein to form a bubbledispersion solution; and curing the bubble dispersion solution.

In this producing method, a polyol compound forming polyurethane, achain-extension agent and a polyisocyanate compound are mixed to form abubble dispersion solution, and the solution, as it is, is cured.

The amount of addition of the surfactant is preferably set in a rangefrom 1 to 20% by weight with respect to the total amount of the firstand second components.

In a preferable mode of the present invention, the above-mentioned mixeris provided with a first mixer blade and a second mixer blade havingshaft centers in the vertical direction, and the first and second mixerblades are designed to rotate in reversed directions in a manner so asto engage each other, and also designed so that the two blades do notinterfere with each other; thus, a gas is involved in the solutionthrough rotations of the mixer.

The mixer having such a structure is used for foaming and mixingprocesses. Moreover, by involving a gas such as air in the solutionthrough the rotations of the mixer blades, fine bubbles can be formed.

In another preferable mode of the present invention, a step of raisingthe first and second mixer blades from the solution face is preparedafter the second step, and at this raising process, the solution thathas adhered to the first and second mixer blades is allowed to flowdownward along the blade portions.

When, upon raising the mixer blades, the solution that has adhered tothe mixer blades drops onto the solution face with splashes, air voidstend to occur to cause degradation in the quality. Therefore, thisarrangement in which the solution is allowed to flow downward along theblade portions makes it possible to allow the solution to flow onto thesolution face smoothly and consequently to prevent the occurrence of airvoids.

The polyurethane foam formed through the producing method of the presentinvention has an average cell diameter in a range from 10 to 70 μm withthe number of cells in a range from 100 to 700/mm², and is preferablyutilized as CMP polishing-use pads and glass polishing-use pads.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view that shows a structure of a manufacturing deviceof a polishing pad-use polyurethane foam;

FIG. 2 is a plan view that shows the structure of the manufacturingdevice of a polishing pad-use polyurethane foam;

FIG. 3 is a side view that shows a structure of a mixer; and

FIG. 4 is a plan view that shows the structure of the mixer.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figures, the following description will discuss preferredembodiments of a manufacturing device of a polishing pad-usepolyurethane foam in accordance with the present invention. FIG. 1 is aside view that shows an external structure of a manufacturing device.FIG. 2 is a plan view that shows a structure of the manufacturingdevice. This manufacturing device aims to obtain a polyurethane foamthrough processes in which a prepolymer and a foaming agent togetherwith an active hydrogen-containing compound dissolved therein arecharged into a tank so as to be foamed and mixed with one another.

This device is provided with a tank 1 used for forming a mixed solution,a mixer 2 used for foaming and mixing the solution in the tank, and amold 3 to which the solution that has been subjected to the mixingprocess is injected.

A guide strut 5 on which the mixer 2 is moved upward and downward isinstalled, and a chain 4 by which the mixer 2 is suspended and abalancer 6 are also installed. By operating a handle (not shown), themixer 2 is moved upward and downward. The tank 1 is also attached to andsupported by another strut through a supporting arm 8 having a virtuallyC-letter shape in its plan view. The mold 3, which is mounted on asupporting base 10 so as to be supported thereby, is allowed to slide ina direction perpendicular to the drawing face of FIG. 1.

The following description will discuss a structure of the mixer 2 indetail. FIG. 3 is a side view that shows the structure of the mixer, andFIG. 4 is a plan view that shows the structure of the mixer. This mixer2, which is a two-axle type mixer, is provided with a first mixer blade11 and a second mixer blade 21. The first and second mixer blades 11 and21 have respective rotary shafts 12 and 22, and as shown in FIG. 4, thefirst mixer blade 11 rotates anticlockwise and the second mixer blade 21rotates clockwise. Each of the mixer blades 11 and 21 is provided withblade portions that are placed along the circumferential direction withthe same intervals (90° pitches). The blade portion of the first mixerblade 11 and the blade portion of the second mixer blade 21 are allowedto rotate in a manner so as to engage each other, with a phase offset of45° from each other, as shown in FIG. 4; thus, these blades are allowedto rotate without interference with each other. Here, in the exampleshown in the Figures, four blade portions are prepared; however, astirring process is available as long as at least two blades areprepared.

As shown in FIG. 3, each of the blade portions has the same shape, suchas an arc shape or an elliptical arc shape, or a predetermined smoothlycurved shape.

With respect to the shape of the tank 1, the diameter is preferably setto several times longer than the outer diameter of each of the mixerblades 11 and 21, and the height is preferably set to such a level thatthe solution does not overflow at the time of the mixing process by themixer. Supposing that the size of a block to be molded is 700 (mm)×150(mm)×30 (mm), the required volume (capacity) of the tank 1 is 31.5 L(liters).

Upon completion of the stirring and mixing processes of the mixer 2, itis necessary to raise the mixer blades 11 and 21 from the mixed solutionin which these have been located; and at this time, the solution thathas adhered to the mixer blades 11 and 21 is allowed to flow downthrough the shape of each of the blade portions without dropping ontothe solution face with splashes.

<Manufacturing Process>

The following description will discuss manufacturing processes of apolyurethane foam in the above-mentioned producing device. Thispolyurethane foam, which is used as CMP polishing pads, needs to have aneven material quality and little deviations in the specific gravitydifference among molded products.

The standard blends are: 1 to 20 parts of SH-192 (made by Dow CorningToray Silicone Company, LTD.) serving as a foaming agent (surfactant)and 26 parts of methylene bis-(O-chloroaniline) (MBOCA) (made by IharaChemical Industry Co., Ltd.) (120° C.) serving as an activehydrogen-containing compound are added to 100 parts of adiprene L-325(made by Uniroyal Chemical Co., Ltd.) (70° C.) serving as anisocyanate-terminated prepolymer.

MBOCA in which specified amounts of adiprene L-325 and SH-192 have beendissolved is charged into a tank 1 and stirred and mixed (mixed so as tobe foamed) by a mixer 2. The number of revolutions in each of the mixerblades 11 and 21 is preferably set in a range from 500 to 3000 rpm. Themixing time is preferably set to about several minutes. This stirringprocess allows air to be involved in the mixed solution.

Here, with respect to the order in which adiprene L-325, SH-192 andMBOCA are charged into the tank 1, these materials may be chargedsimultaneously, or some of these are first charged thereto and stirredand mixed, and after a lapse of predetermined time, the rest of them maybe charged thereto and stirred and mixed.

After completion of the stirring process, the mixer blades 11 and 21 areraised from the solution. At this time, the solution that has adhered tothe mixer blades 11 and 21 is allowed to flow down through the shape ofeach of the blade portions. Therefore, it becomes possible to preventthe occurrence of air voids due to dropped solution with splashes. Afterthe mixer blades 11 and 21 have been raised from the solution, the mixedsolution is poured into a mold 3 immediately before the viscosityincreases.

A general method for pouring the mixed solution into the mold 3 is amethod in which the tank 1 is tilted so as to pour the mixed solutioninto the mold 3. In a more preferable method, a valve (not shown) isattached to the bottom portion of the tank 1 so that the mixed solutionis poured into the mold 3 from the bottom portion. The latter method ismore preferable because this method is less susceptible to theoccurrence of air voids.

Upon producing a polyurethane foam, the following specific gravityadjusting method is carried out. Supposing that the capacity of the tank1 up to the position of the uppermost portion of each of the mixerblades 11 and 12 set inside the tank 1 is defined as 100, by chargingthe solution to the position corresponding to capacity 80, it becomespossible to obtain a block of about 0.8 (g/cm³) when the solutionspecific gravity is 1.

The properties of the polyurethane foam obtained as described above areexplained as follows:

Specific gravity . . . 0.4 to 0.9 g/cm³

Hardness (Shore D) . . . 30 to 60

Average cell diameter . . . 10 to 70 μm

Number of cells . . . 100 to 700/mm²

EXAMPLE 1

In the case when 24.1 kg of adiprene L-325, 0.73 kg (about 3 parts) ofthe foaming agent SH-192 and 6.32 kg of MBOCA were used, a block havinga specific gravity of 0.845 was obtained. At this time, its Shore DHardness was 54.

EXAMPLE 2

In the case when 21.4 kg of adiprene L-325, 0.81 kg (about 4 parts) ofthe foaming agent SH-192 and 5.6 kg of MBOCA were used, a block having aspecific gravity of 0.781 was obtained. At this time, its Shore DHardness was 51.

Another Embodiment

With respect to the shape of each of the mixer blades, not particularlylimited by the shape of the present embodiment, various modificationsmay be made within the scope of the present invention.

The polyurethane foam thus produced may be used not only for CMPpolishing pads, but also for glass polishing pads.

1. A method of producing polishing pad-use polyurethane foam comprisingthe steps of: charging a first component, a foaming agent and a secondcomponent that reacts with the first component to form polyurethane inspecified amounts into a tank and foaming/mixing them for a specifiedtime by a mixer; and after the above-mentioned step, pouring the mixedsolution into a mold so as to react with one another to be cured,wherein the mixed solution is poured into the mold through a valveattached to a bottom of the tank.
 2. The method of producing a polishingpad-use polyurethane foam according to claim 1, wherein the mixercomprises a first mixer blade and a second mixer blade having shaftcenters in a vertical direction, and the first and second mixer bladesare allowed to rotate in reversed directions in a manner so as to engageeach other, and are also designed so that the two blades do notinterfere with each other so as to allow a gas to be involved in thesolution through rotations of the mixer.
 3. The method of producing apolishing pad-use polyurethane foam according to claim 1, furthercomprising a step of raising the first and second mixer blades from thesolution face after the second step, wherein at this raising process,the solution that has adhered to the first and second mixer blades isallowed to flow downward along the blade portions.
 4. A polyurethanefoam, produced through the producing method disclosed in claim 1,wherein an average cell diameter is in a range from 10 to 70 μm and thenumber of cells is set in a range from 100 to 700/mm².
 5. The method ofproducing polishing pad-use polyurethane foam according to claim 2,wherein the number of revolutions in each of the mixer blades is set ina range from 500 to 3000 min−1.
 6. A manufacturing device forpolishing-pad-use polyurethane foam comprising: a tank to which apolyurethane foam-forming composition is charged; and a mixer whichfoams and mixes the composition charged into the tank, wherein: themixer comprises a first mixer blade and a second mixer blade havingshaft centers in a vertical direction, and the first and second mixerblades are allowed to rotate in reversed directions in a manner so as toengage each other, and are also designed so that the two blades do notinterfere with each other; each of the first and second mixer blades isconstituted by a plurality of blade portions; and a mold is installed ata bottom of the tank so that a mixed solution is injected into the moldthrough a valve attached to the bottom.
 7. The manufacturing device forpolishing-pad-use polyurethane foam according to claim 6, wherein eachof the blade portions has a smooth shape, and an upper end and a lowerend of the blade portion are supported by a rotary shaft.
 8. Themanufacturing device for polishing-pad-use polyurethane foam accordingto claim 6, wherein the blade portions are formed into such shapes thatupon raising the first and second mixer blades from the solution face,the solution is allowed to flow downward along the blade portionswithout causing splashes.
 9. The manufacturing device forpolishing-pad-use polyurethane foam according to claim 6, furthercomprising: a guide strut on which the mixer is moved upward anddownward; a chain on which the mixer is suspended; and a balancer thatsupports the weight of the mixer.
 10. A method of producing apolyurethane foam comprising: loading a first component, a foamingagent, and a second component that reacts with the first component toform polyurethane into a tank; mixing and foaming the first and secondcomponents and the foaming agent in the tank; and pouring the resultantmixture into a mold from a bottom of the tank, thereby curing themixture, said mold being disposed underneath the tank.
 11. The methodaccording to claim 10, wherein the mixing is conducted using a firstmixer blade and a second mixer blade having shaft centers in a verticaldirection.
 12. The method according to claim 10, wherein the first mixerblade and the second mixer blade have smoothly curved shapes tofacilitate a portion of the mixture adhering to the blades to flow downalong the blades and drip into the mixture without splashes when theblades are separated from the mixture.
 13. The method according to claim10, wherein the first component contains an isocyanate-group-containingcompound, the second component contains an active hydrogen-containingcompound, and the foaming agent is a silicon-containing nonionicsurfactant having no hydroxide group.